Electrophysiological studies are being done to investigate the mechanism(s) of ion transport in epithelial tissues including the renal tubule and anuran tissues. Studies of frog skin with intracellular microelectrodes are being done to determine the electrical properties and the origin of the voltages at apical and basolateral barriers of the Na transporting cells. Additional studies are to be done with intracellular ion specific microelectrodes to assess the concentrations of K and Cl under normal and altered conditions of Na transport of intact and split skins. The chronic effects of DOCA are being studied in isolated cortical collecting tubules with special emphasis on the mechanism of N ion secretion and its relationship to the luminal concentrations of Na and K. Studies are also to be done to investigate the chronic effects of DOCA pretreatment of rabbits on the NaCl absorption of the thick ascending limbs of Henle.